The cells of Streptococcus mutans are able to adhere tenaciously to smooth surfaces and form large aggregates in the presence of sucrose, characteristiCs reflecting the ability of this cariogenic organism to form dental plaque. The biochemical mediators of adherence and aggregation reside in a group of glucan-synthesizing enzymes (glucosyltransferases, GTF) and glucan-binding proteins. The complex structure of the water-insoluble glucans implicated in cell adherence and plaque formation appears to result from the actions of several glucan-synthesizing enzymes. Four distinct glucosyltransferases have been identified in S. mutans strain 6715 with monoclonal antibodies: Two GTF synthesizing water-soluble glucans (isozymes GTF-S1,S2 and GTF-S4) and two synthesizing water-insoluble glucans (isozyme pairs GTF-11,13 and GTF-12,14). The GTF-S enzymes are completely distinct immunologically, synthesize markedly different 1,6-Alpha-D-glucans and have different requirements for primer dextran. The GTF-I enzymes share some determinants but can be differentiated with monoclonal antibodies and appear to produce different water-insoluble glucans. We have found that Streptococcus mutans also produces a dextran-branching enzyme capable of forming branches in the absence of sucrose, the first such enzyme reported. Together, the GTF isozymes and the branching enzyme have the potential to form the complex extracellular glucans characteristic of S. mutans. Thic complex group of glucan-synthesizing enzymes is complemented by several glucan-binding proteins, which seem to lack enzyme activity. Some of these proteins are major components of the extracellular protein complement and may serve as cell-surface sites for specific binding of glucan during adherence and aggregation. Streptococcus mutans has long been known to produce endodextranase, an enzyme which degrades 1,6,-Alpha-D-glucans, inhibits glucan synthesis by S. mutans enzymes, and blocks sucrose-dependent cell to surface adherence. However, S. mutans strains which produce endodextranase also produce a potent but reversible inhibitor of endodextranase, which appears to be an extracellular means for modulation of endodextranase activity. The studies proposed and outlined here are directed to the determination of the roles of these several proteins and enzymes in the processes of glucan synthesis and cell adherence by S. mutans. To this end, we are developing panels of monoclonal antibodies specific for and capable of inhibiting the function of each of these proteins.
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